1. Field of the Invention
The present invention relates to a correction apparatus for correcting warping of a plate-like workpiece such as a frame unit which has been cut out from a flexure chain blank sheet for example, and a warp correction method.
2. Description of the Related Art
A hard disk drive (HDD) is used in an information processing apparatus, such as a personal computer. The hard disk drive comprises a magnetic disk rotatable about a spindle, carriage turnable about a pivot, etc. On an arm of the carriage, a disk drive suspension (which will be hereinafter simply referred to as a suspension) is provided. The suspension comprises elements such as a load beam, and a flexure disposed to overlap the load beam. A magnetic head including a slider is mounted on a gimbal portion formed near a distal end of the flexure. The magnetic head is provided with elements for accessing data, that is, for reading and writing data. The load beam and the flexure, etc., constitute a head gimbal assembly.
Various types of flexures have been put to practical use according to the required specification. As an example of the flexure, a flexure with conductors is known. The flexure with conductors includes a metal base made of a thin stainless steel plate, an insulating layer made of an electrically insulating material, such as polyimide, which is formed on the metal base, and a plurality of conductors formed on the insulating layer.
Conventionally, as a means for enhancing the manufacturing efficiency of the flexure, a flexure chain blank sheet disclosed in, for example, JP 5,273,271 B (Patent Literature 1) and JP 5,365,944 B (Patent Literature 2) is known. In order to manufacture the flexure chain blank sheet, a number of flexure elements having the same shape are formed by etching a single stainless steel plate, for example. Further, a conductive circuit portion is formed on each of the flexure elements.
The flexure chain blank sheet is constituted by arranging a plurality of frame units longitudinally or laterally relative to the sheet. Each of the frame units which constitute the flexure chain blank sheet comprises a frame portion and a number of flexure elements arranged at predetermined pitches within the frame portion. In this specification, of the front side and back side of the frame unit, the side on which the conductive circuit portion is provided is referred to as a first surface, and the side opposite to the conductive circuit portion is referred to as a second surface.
The flexure chain blank sheet is cut off for each of the frame units in the manufacturing process of a flexure. That is, a plurality of frame units are cut out from a single flexure chain blank sheet. A frame unit cut out from the flexure chain blank sheet is an example of a plate-like workpiece. For each of the flexure elements provided in the frame unit, operations such as bending processing and mounting on a load beam are performed.
Stress produced in the process of manufacture may remain in the flexure chain blank sheet. Also, by a difference in the thermal expansion or moisture absorptivity, etc., between the conductive circuit portion and the metal base, there are cases where stress remains in the flexure chain blank sheet. Accordingly, even if the flexure chain blank sheet looks straight and planar at a glance, stress is released when the frame unit is cut out from the flexure chain blank sheet, or the flexure elements are individually cut off from the frame portion of the frame unit, which causes the flexure elements to warp. In particular, the first surface (the side on which the conductive circuit portion is provided) may have slight concave warping. Such warping may be called a “recessed warp”.
For example, when some kind of process is to be performed for the flexure element while the conductive circuit portion of the flexure element is made to face upward, pins may be inserted into positioning holes formed near both ends of the flexure element, respectively. However, when the flexure element has the aforementioned “recessed warp”, the positioning accuracy is degraded, such as pins which are inserted into the positioning holes tending to detach easily. Accordingly, depending on a process of handling the flexure element, it is sometimes more convenient if the first surface (the side on which the conductive circuit portion is provided) warps with the first surface being convex (i.e., to have the so-called upward warp).